Resolution of mtxtures of- jjeterjq-



Patented June 3, 1947 Q IC NITR E ;,Karl Henry Engel, Teaneck, N. J., assignon to Allied Chemical Dye Corporationa-Nevv York, @N a, Y a corporation of New:,ork

No Dr wih A p io Wqbh 9494.2

" fiehie -tfihilh 7 Claim :1 This invention relates to the resolution of pyrrolepicoline fractions, particularly to the separation of spy'rrole from such fractions.

The .picolines, other homologs ofpyridine-and pyrrole are customarily extracted from coke oven solution of amineral-acid, usually sul-furic acid.

.After liberation from.these acid solutions by "means of alkali, the mixtures of nitrogen compounds are fraotionally distilled. -l3ases suchas pyridine, boi1ing-point 116 C., and 2-picoline, boiling point 129.4 C., oangenerally be obtained in reasonably pure form by fractionaldistillation, but for the most part the remaining compounds .cannotbeseparated lay-distillation methods alone. Instead, the fractions obtained even when they are. of relatively narrow boiling range, contain increasing numbers of pyridine homologs and their isomers.

1 Fractions of heterocyclic nitrogen compounds recovered from certain coaltars containing substantial proportions of pyrrole, boiling withinthe range 1.4.0'-148 0., even close-cut fractions boiling within the range 145148 C., contain in substantial proportions 3-picoline (heta p icol i ne) boiling point 143.8 C.,- 4-picoline (gamma-picoline), boiling point 144.8 (3., generally a sn all amount .of 2,6-lutidine, boiling point -11l3=8 and, in addition,.a.sub stantial quantityof pyrrole. Although pyrrolealone" boils at 12 9 .8 "Cg-with 3- andA-picolines it forms high boiling azeotropes boiling about 145-148 0., the components of wh are inseparable vby. ii i h! iqh 11.1 .19 0.( Mixtures of this kind have found limited-practical application mainly'as special solygnts i re of relatively low economic value. The individual compounds; however -if they could be readily isoe lated, would be of far greater value, particularly in the preparation of derivatives. For egrarnple, pyrrole .derivatives are of importance as pharmaceufieals d a ult a sh mf els -ea insecticides; 3-pico1ine is of importance as raw material for production of nicotinic aci d a member of the vitamin'B complex, and derivativesgf all these-bases are of value in the preparation ,of dyes and medicinal products.

Sincethe componentsrnaking up the heterocyclic nitrogen compound'fractions boiling in the range 140148Q."either have suhstanti ally the saine boiling points or, as thei case of pyrrole, form azeotropes with these bases, fractional distillation is obviously unsatisfactory as arneans ior resolving the mixtures. Other "meth d q resolving such mi gtures heretofore lgnovvn have 2 been generally unsatistactory in regard to 'products yields, andproduction costs. Such other rnethods have usually depended upon-fractional crystallization of the more common salts .distillates and othersourcesof these h eterocyoli c nitrogen compounds by means of an-aqueous of the bases present, e. g th e sultates/ozgalates, chlorates, picrates; ferroeyanides, and 'the -like.

' o a i rhurifi at on. h ish h hmu ids Such m h d ha b en h dt be e tremel um rs m nd ehs thl iin u z sht sh r to obtain compounds of a purity demanded in industry. Thesemethods also have otten vpresented other-drawbacks such as prohiloitiveicost, explosion hazardshand toxicity.

is an ofhi n eh ih t rmvisl re e s a e hg pur p r l PI.PYII'Q1- enriched iractions from admixture ,with other i r yeh .h q h .som oh ds 9 i ep ab her omby d i ation- It is 'tu h r Qhiht o thi i vhhtio t md mm ie l x eas le metho fo resol n tures of pyrroles andother heterocyclic nitrogen compounds not se a a leitem.h rm hvr i tili ic-flash r; oth mpoun s shche 3 nic w -r hh :Zfirlhhdihh.byi hhhiha inc chloride di on ommend of the hs rhc ql t o en om n .,.,h tha n rro s a t a t s pa a i s-th hrrrs eithe z rdistilhen or by fi t hhhifr mzth h sia iheo z n ehloride i io c m ound Yfi iqli fil llfl o le mti ih y ,e hs xioe i otiorhha. zi or d a t o @Qh wh hr i hhsh ermin- Stable sqh qvhd of tha t e homharss t th d t n com uhd rmsd bro he het ro cl tr en q m w not se a abl gf mr wml v sti h- Th mix ur Hem whi th pyrrole is separated in accor dance with my inve ma ad n ag us h acb ewu iracti n f h t roc c'nitro en, qommanq r. a. o k o e ori n b i in in; he ran e .l. .1r18 o t in a pri i a hQmQ hen -ry role. -pico1ine. an -I. i ;o ,e w th vsh ih le am n s ora ut slih M in s tiqnma thu m ris r het ha hete c chc nitroge m qhhd ixtur ,ch ehi h .Pvrr 1 a d p hdine homolqgsto ql tain' su oh a clo s cnt fraohon. ifr q ih b i ing r dhminahtl m hi he .ra ,0 CC, se aratin yh rr l fQIn vth s, t act o afte iormihs .z h hhl ride addition compounds of the other heterocyclic nitrogen compounds present.

My invention further comprises a process in which separation of pyrrole is combined with steps for isolation of the other heterocyclic nitrogen compounds present with pyrrole in these close out fractions. Thus my invention is applicable to resolving into its components a mixture of pyrrole, B-picoline, 4-picoline, and 2,6-lutidine.

The process of my invention may advantageously be applied to the resolution of the heterocyclic nitrogen compound mixtures obtained from coke oven distillates, cracked petroleum, shale tar, bone oils and from other natural, as well as synthetic, sources when these base mixtures contain substantial amounts of pyrrole and other nitrogen compounds not readily separable therefrom by distillation, e. g., 3-picoline, 4-picoline, and 2,6-lutidine. As above pointed out, in carrying out the process of my invention, such a mixture is first subjected to fractional distillation whereby a fraction of boiling range 140- -148 0., containing predominantly pyrrole, 3-picoline and 4-picoline, is obtained.

In carrying out the process of my invention, a pyrrole fraction as above described, suitably a fraction of boiling range 140-148 0., containing pyrrole, 3-picoline, 4-picoline and small amounts of 2,6-lutidine, is treated with zinc chloride. The zinc chloride is preferably employed in amount sufficient to react with heterocyclic compounds other than pyrrole, i. e., with the above-mentioned pyridine homologs, to form addition compounds in which two mols of nitrogen compound are combined with one mol of zinc chloride. Alternatively, in treating a 3-picoline-4-picoline- 2,6-lutidine-pyrrole mixture, an amount of zinc chloride suificient to combine only with the picolines may be used, in which case the original mixture will be separated into a 3- and l-picoline fraction, and lutidine-pyrrole fraction, each of which may be further resolved, as will be described below. Any convenient working temperature up to about 50 0., e. g., the normally prevailing room temperature, may be employed in reacting the zinc chloride with the nitrogen compounds.

After treatment with zinc chloride reagent, the pyrrole of pyrrole and lutidine components may be removed, either by steam distillation of the mixture or by cooling to crystallize the zinc chloride addition compounds which are then filtered 01f, e. g., by centrifuging. When the zinc chloride addition compounds are to be removed by crystallization and filtration, the crystallization is preferably carried out in the presence of a diluent such as water, methanol or ethanol. Further diluent may be added after crystallization, if necessary, for ease in handling the mass.

When the separation is carried out by steam distillation, as above described, a somewhat less sharp separation is obtained than with the crystallization method. The organic component of the distillate from the steam distillation will generally consist predominantly of pyrrole and contain, in addition, small amounts of 2,6-lutidine and 3- and 4-picolines. Such distillates may be subjected to additional zinc chloride treatments, in each case adding the required amount of zinc chloride to react with the picolines and lutidine present, and again steam distilling. With two such additional zinc chloride treatments and steam distillations, I have found a substantially pure pyrrole may be obtained as distillate. When a number of successive zinc chloride treatments and distillations are thus carried out, the 2,6- lutidine component of the original fraction will be found concentrated in the residues from these additional zinc chloride treatments and distillations, while the residue from the first zinc chloride treatment and distillation will contain substantially only the 3- and l-picoline addition compounds.

The various zinc chloride addition compounds recovered either as precipitates or as distillation residues may each be treated to recover the free base, for example by treatment with an aqueous solution of an alkali, preferably sodium hydroxide, or a sodium carbonate solution. The zinc oxide or carbonate which precipitates in these base liberation operations may be reconverted to zinc chloride by adding the stoichiometric quantity of hydrochloric acid and may then be reused in the process.

A 3- and 4-picoline mixture may thus be recovered and may be further resolved by precipitating 4-picoline in the form of its calcium chloride addition compound, or by precipitating 3- picoline in the form of its phosphate, or by a combination of both of these steps, as disclosed in copending application Serial No. 441,557, filed May 2, 1942. When the concentration of 3- picoline is sufiiciently high, i. e., above about 50%, a substantial part of the 3-picoline may be precipitated directly as pure phosphate.

When the lutidine fraction recovered as above described contains small amounts of picolines, this mixture may also be resolved, as described in the copending application above referred to, or a pure 2,6-lutidine may be precipitated as phosphate in accordance with the process of my copending application Serial No. 346,347, filed July 19, 1940.

Thus by separating pyrrole as above described and combining therewith other operations such as the separation of 3-picoline and 2,6-lutidine as phosphates described in the above copending applications, pyrrole fractions containing picolines and 2,6-lutidine may be resolved into their components.

The following example is illustrative of the process of my invention:

The material used in this example consisted of a mixture of heterocyclic compounds having a boiling range of 142145 0., bulb distillation. Its composition was approximately as follows:

Per cent 3-picoline 42 4-picoline--approximately 33 Pyrrole 19 the remainder of the material consisting of 2,6- lutidine and traces of 2,4-lutidine.

1000 parts by weight of this material were placed in a still pot. A solution of 700 parts by weight of zinc chloride in 700 parts of water was gradually added with agitation of the mass. The resulting zinc chloride-picoline addition compound and pyrrole formed a slightly viscous solution. The still charge was steam distilled. Distillates separated in an upper layer consistin of pyrrole and pyridine homologs with dissolved water and a lower, predominantly aqueous layer.

The latter product was intermittently returned to the still charge, until a total of 285 parts by weight of the pyrrole-containing distillate had been collected. ,The material contained approximately 40% of pyridine homologs. It was mixed with 200 parts by weight of a solution containing parts of zinc chloride. The mixture was steam distilled as .before until 175 parts by weight of pyrrole concentrate had been obtained. This material still contained approximately of pyridine homologs.

It was therefore mixed with 100 parts by weight of a 50% solution of zinc chloride and steam distilled for a third time. The operation yielded 148 parts by weight of pyrrole, containing 2% of pyridine homologs by the method of analysis employed, i. e., acidimetric titration with standard hydrochloric acid solution. An extrac tion with a dilute solution of oxalic acid removed the last traces of heterocyclic bases. The material thus distilled consisted of pure pyrrole having a boiling point of 129.8 C.

The distillation residues of the last two purifications were combined, treated with sodium hydroxide solution, and steam distilled to recover by-product heterocyclic bases, 70 parts by weight of dehydrated product being obtained. The material thus recovered contained 70% 2,6-1utidine, besides 3- and 4-picolines.

The first still residue, consisting of zinc chloride compounds with 3- and 4-picolines and water, was allowed to settle at 80 C., the mixture settling in two liquid layers. The upper aqueous layer was taken off. The zinc chloride compound was washed twice with 350 parts of hot water to remove additional soluble by-product bases, the picoline addition compounds showing only a small solubility.

The residual compound was decomposed by addition of sodium hydroxide in 30% aqueous solution. Liberated bases were steam distilled. separated from solution by saturation with sodium chloride, dehydrated and distilled, 538 parts by weight of a picoline mixture being obtained. The mixture was found to have the following composition:

Per cent 3-picoline 54 4-picoline 43 2,6-lutidine 2 In addition, the material contained a trace of residual pyrrole.

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limit ing sense.

What is claimed is:

In a process for separating pyrrole from a mixture thereof with pyridine homologs not readily separable therefrom by distillation, the steps which comprise treating the mixture with zinc chloride to form addition compounds with the pyridine homologs and separating pyrrole from the addition compounds thus formed.

2. A process for recovering pyrrole from mixtures of pyrrole with 3-picoline and 4-picoline which comprises treating the mixture with zinc chloride in amount suflicient to form addition compounds with all heterocyclic nitrogen compounds other than pyrrole and separating pyrrole from addition compounds thus formed.

3. A process for recovering pyrrole from mixtures of pyrrole-with 3-picoline and 4-picoline which comprises treating the mixture withqzinc chloride in amount sumcient to form addition compounds with all heterocyclic nitrogen compounds other than pyrrole and separating pyrrole by steam distillation from the addition compounds thus formed.

4. A process for recovering pyrrole from mixtures of pyrrole with 3-picoline and 4-picoline which comprises treating the mixture with zinc chloride in amount sufficient to form addition compounds with all heterocyclic nitrogen compounds other than pyrrole, crystallizing the addition compounds thus formed and separating the crystals from the uncombined residue rich in pyrrole by filtration,

5. A process for resolving a mixture of heterocyclic nitrogen compounds containing pyrrole and pyridine homologs which comprises fractionally distilling said mixture to obtain a distillate cut containing a substantial amount of pyrrole and of pyridine homologs not readily separable from pyrrole by distillation, treating said out with an amount of zinc chloride sumcient to form addition compounds with the pyridine homologs, and separating the pyrrole-rich uncombined residue from the addition compounds thus formed.

6. A process for resolving a mixture of heterocyclic nitrogen compounds conrtaining substantial amounts of pyrrole, 3-picoline and 4- picoline, comprising treating said out with an amount of zinc chloride sufficient to form addition compounds with the pyridine homologs, separating the pyrrole-rich residue from the addition compounds thus formed, treating the addition compounds to liberate free base, and treating the free base thus liberated to isolate 3- picoline as phosphate.

'7. A process for resolving a mixture of heterocyclie nitrogen compounds containing substantial amounts of pyrrole and of pyridine homolcgs not readily separable from pyrrole by distillation, comprising treating said out with an amount of zinc chloride sufficient to form addition compounds with the pyridine homologs, subjecting the reaction mixture to distillation to separate a pyrrole-rich distillate, treating this distillate with additional zinc chloride to comblue with residual pyridine homologs contained therein to form addition compounds, and recoverin'g substantially pure pyrrole from the reaction mixture treated with the additional zinc chloride.

KARL HENRY ENGEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Mahan and Bailey, Journal Amer. Chem. Soc. (1937), vol, 59, page 449 and following.

Journal American Chem. Soc., vol. 43, pages- 1936-1940 (1921), 260-290A. Journal Chemical Society, vol. 95, pages 668-85. 

